create dataframes and column names using R equivalent of python *args-CodePudding

I learnt that in R you can pass a variable number of parameters to your function with ...

I'm now trying to create a function and loop through ..., for example to create a dataframe.

    create_df <- function(...) {
      for(i in ...){
        ... <- data.frame(...=c(1,2,3,4),column2=c(1,2,3,4))
      }
    }

create_df(hello,world)

I would like to create two dataframes with this code one named hello and the other world. One of the columns should also be named hello and world respectively. Thanks

This is my error:

Error in create_df(hello, there) : '...' used in an incorrect context

CodePudding user response：

It's generally not a good idea for function to inject variables into their calling environment. It's better to return values from functions and keep related values in a list. In this case you could do this instead

create_df <- function(...) {
  names <- sapply(match.call(expand.dots = FALSE)$..., deparse)
  Map(function(x) {
    setNames(data.frame(a1=c(1,2,3,4),a2=c(1,2,3,4)), c(x, "column2"))
  }, names)
}

create_df(hello,world)
# $hello
#   hello column2
# 1     1       1
# 2     2       2
# 3     3       3
# 4     4       4

# $world
#   world column2
# 1     1       1
# 2     2       2
# 3     3       3
# 4     4       4

This returns a named list which is much easier to work with in R. We use match.call to turn the ... names into strings and then use those strings with functions that expect them like setNames() to change data.frame column names. Map is also a great helper for generating lists. It's often easier to use map style functions rather than bothering with explicit for loops.